The present invention generally relates to transmitting communication signals in radio frequency energy beams in wireless communication systems and, more particularly, to time sharing of radio frequency energy beams among a number of different communication channels.
Communication systems on modern satellites and other wireless communication platforms often employ a large number of narrow spot energy beams for communicating radio frequency (RF) signals. The narrower the spot beam, the smaller the user's antenna can be for a given bit rate, or data speed, to be effectively communicated. In a typical such communication system, the wireless communication platform has fewer communication paths (each path corresponding to a transponder) than the number of spot beams, and therefore the paths are time-shared. This time-sharing goes by the name of beam hopping, since conceptually a limited number of active beams are hopping around to serve a larger number of cells. A switch network typically performs the hopping function, selecting a communication path (or no communication path) for each cell, with the selections changing rapidly as the beams hop.
High-power RF signals are difficult to switch rapidly. Even a small insertion loss in the switch element can cause the switch element to heat rapidly and fail. With power levels above a few watts, switchable circulators containing ferrite are typically used. An electrical current pulse switches the magnetization of the ferrite and hence the direction of the circulation, directing the RF signal to either the left or right output port of the circulator. The basic switch element is thus equivalent to a single pole, double throw (SPDT) switch in the waveguide.
A small switch network was included in the Advanced Communications Technology Satellite (ACTS) Ka-band satellite, which was recently decommissioned. The ACTS ferrite switch network was relatively small with only two active beams hopping over 30 and 18 cells, respectively. Nevertheless, the packaged network was relatively bulky. In addition to ACTS, similar ferrite switch networks have been flown on non-commercial satellites.
As can be seen, there is a need in wireless communication systems for the outputs from several high-power amplifiers to be time-shared among a larger number of cells. Moreover, there is a need for a switch network the packaging of which is efficient enough to support 100 or more cells within a mass and size that are practical for a satellite or stratospheric platform payload.